The present invention relates to a composite hanger grid for supporting splash bars in a cooling tower, components of the composite hanger grid, splash bars adapted for use with specific embodiments of the composite hanger grid, assemblies of the composite hanger grid with its supported splash bars, a method of assembling a composite hanger grid and a method of assembling an evaporative cooler fill assembly, including hanger grids and splash bars, in a cooling tower.
Cooling towers are open loop direct contact evaporative heat exchangers used to provide a heat sink for a wide variety of waste heat applications. Hot process water is delivered to the cooling tower via nozzles from above. The water from the nozzles is distributed and cascades over the media typically called “fill” which provides surface area from both the droplet and a structure for mass transfer and subsequently latent heat removal. Air delivery is through either natural draft or forced ventilation. Depending on the direction of air flow through the cooling tower with respect to the cooling liquid, typically water, the cooling tower may be concurrent (air and water flow in the same downward direction), which is rare due to less turbulent interaction of the air and water, counter-current (water flows downwardly and air flows upwardly), or cross-flow (water flows downwardly and air flows sideways). The composite hanger grids, components, splash bars and assemblies thereof according to the present invention may be used with any of these types of cooling towers, preferably with counter-current and cross-flow cooling towers.
The tower fill utilized depends upon the tower application, which varies widely based on many factors. For instance, a splash fill is typically used for applications where the water source contains solid impurities or fouling is expected. A number of variations exist for tower fill including splash fill that relies on the impact of falling water on a surface to provide relatively small water droplets of high surface area to volume ratios. Fill surface area also contributes to the mass transfer capacity. Splash bars are a variation of splash fill that requires a support system to position the splash bars at the appropriate location in the cooling tower for proper operation. As the name suggests, splash bars are generally longitudinal shaped bars or beams that must span support members within the cooling tower where the spacing between supports is typically 2 feet. Splash bars themselves vary in length and shape, but are generally limited to 12 feet in length and five 5 inches in width for ease of assembly.
The splash bars are offset both vertically and horizontally so that water droplets falling vertically from near the top of the cooling tower will invariably strike one or more of the splash bars below the water distribution system and from higher splash bars onto lower splash bars during descent. Large water droplets are broken into smaller water droplets upon striking one of the splash bars. As many water droplets strike the splash bars, a thin film of water tends to form on each splash bar which increases the surface area of water exposed to air to enhance evaporative cooling.
Typical prior art splash bar support grids, called hanger grids, are a mesh of perpendicular members usually spaced at fixed dimensions of 4 inches horizontally and either 4 or eight 8 inches vertically to form windows within which the splash bars are supported on the horizontal members. The hanger grids having 4-inch vertical spacing are installed at the top of a cooling tower (near the fan in the case of a mechanical-draft tower) to prevent excessive localized air velocities and create an even pressure drop throughout the cooling tower, when hanger grids having 8-inch vertical spacing are installed toward the middle and bottom of the cooling tower. The grids formed by the mesh are generally 2 or 4 feet in width and 4, 6 or 8 feet in height. The hanger grids can be sized to fit within a fill section where air and water interact within cooling towers of various designs and dimensions.
Currently, splash bars are supported by one of several accepted methods. The first method utilizes a wire mesh grid with horizontal and vertical wire members that are spot welded at the crossing points and treated for corrosion resistance. One treated version uses a dipped plastic coating; however, the vibration and movement of the splash bars within the tower from air flow causes localized wearing of the coating at contact points between the grid and the splash bar, thereby exposing the wire to corrosion and ultimately failure of the wire. The second treated version uses galvanized metal; however, chemical treatment erodes the zinc coating leading to a similar local degradation of the material and associated failure mechanism as the coated wire mesh. Stainless steel wire mesh is also used; however, the spot welded connection is typically limiting in its structural capacity and is the point of failure for this application.
Plastic injection molded grids are used to provide a similar spacing arrangement and typically have an integrated connection method for splash bar attachment molded into either the vertical or horizontal members. The plastic grids are generally molded as a single unit of 2 or 4 feet in width and 4, 6 or 8 feet in height. The plastic grids tend to fail at the areas of high stress near the top of the splash grid hanger as the load from the lower levels is additive upwardly on the grid toward the upper connection to the cooling tower structure. As the load increases, the stress in the vertical support members of the grid also increases. The material properties are exceeded locally near the top as the stress surpasses the ultimate strength of the material at the design cross section able to support the load. The current plastic products attach via holes in the vertical members, concentrating the stress at these locations therefore further reducing the strength of the product.
Typical splash bars are slightly greater in width than the 4-inch openings of the support grids to eliminate bypass of the cascading water. As a result, the splash bars must be rotated on edge to be inserted into the hanger grid. Notches punched into one or both edges of the splash bars allow the splash bar to lay flat on the horizontal members of the hanger grid while encompassing the vertical members of the hanger grid. There are problems regarding the installation and retention of the splash bars on the horizontal members. The process of rotating the splash bars in the narrow windows during installation complicates and increases the time required for installation.
The splash bars are typically held in place within the windows of the hanger grids by external clips, opposing clips integrally molded, or large staples (termed “hog rings”). The method of attachment is critical in maintaining the splash bars in position and can have a significant impact on cost due to manpower required to attach the splash bar to the support at every grid location. Commonly, the grids are installed sequentially up to the length of the splash bar. Access is not available from the side or other end. The splash bars are inserted from one end and clipped or stapled at the single exiting end location. This leaves the unattached end of the splash bar to move freely within the grid windows due to the lateral and vertical air flow required for mass transfer. In cases where access is available, increased manpower is required to attach all clip locations of the grid to the splash bars.
Two methods are typically employed to secure hanger grids to the cooling tower structure. With wire mesh support grids, a separate bracket is first fastened to the cooling tower support structure using screws or nails. The wire hanger grid is then hung from the bracket, typically by the top horizontal wire. The load of multiple panels connected together is then applied to the spot welds of the top horizontal wire which may end in failure of the welds, particularly in cold climates where ice may form on the hanger grids and splash bars in winter. Injection molded plastic hangers typically feature nail or screw holes in either the top horizontal member or near the top of the vertical members. The same principle of accumulated load of multiple connected panels also applies to the plastic panels which results in the load surpassing the ultimate strength of the plastic vertical members. Typical top hanging brackets are designed to extend over the top of horizontal structural beams within the cooling tower to “hook” the hanger grid onto the horizontal structural beam. Different beam sizing for major and minor structural support beams for the hanger grids (e.g., structural support beams having different heights, such as 2 inches by 4 inches compared to 2 inches by 6 or 8 inches) cause the top elevation not to have uniform heights within the cooling tower, requiring measurement for exact placement of a rotated hanger grid, where the side opposite the hook is extending away from the structural beam.
The foregoing problems associated with the prior art hanger grids, splash bars and their assembly are overcome by the various aspects and embodiments encompassed by the present invention including a composite hanger grid for supporting splash bars in a cooling tower, components of the composite hanger grid, splash bars adapted for use with specific embodiments of the composite hanger grid, assemblies of the composite hanger grid with its supported splash bars, a method of assembling a composite hanger grid and a method of assembling an evaporative cooler fill assembly, including hanger grids and splash bars, in a cooling tower.